W Luo

Publications (2)17.05 Total impact

• Source

  Available from: Ying-Hao Chu

  Article: Interface control of bulk ferroelectric polarization.

  P Yu, W Luo, D Yi, J X Zhang, M D Rossell, C-H Yang, L You, G Singh-Bhalla, S Y Yang, Q He, Q M Ramasse, R Erni, L W Martin, Y H Chu, S T Pantelides, S J Pennycook, R Ramesh
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  ABSTRACT: The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon.
  Proceedings of the National Academy of Sciences 05/2012; 109(25):9710-5. · 9.68 Impact Factor
• Article: Microscopic origin of the giant ferroelectric polarization in tetragonal-like BiFeO(3).

  J X Zhang, Q He, M Trassin, W Luo, D Yi, M D Rossell, P Yu, L You, C H Wang, C Y Kuo, J T Heron, Z Hu, R J Zeches, H J Lin, A Tanaka, C T Chen, L H Tjeng, Y-H Chu, R Ramesh
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  ABSTRACT: We report direct experimental evidence for a room-temperature, ∼130  μC/cm(2) ferroelectric polarization from the tetragonal-like BiFeO(3) phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.
  Physical Review Letters 09/2011; 107(14):147602. · 7.37 Impact Factor
• Article: An atomic resolution view at oxidation states in transition metal oxide heterostructures

  M. Varela, S. J. Pennycook, T. J. Pennycook, W. Luo, S. T. Pantelides, J. Garcia-Barriocanal, F. Y. Bruno, C. Leon, J. Santamaria
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  ABSTRACT: In LaMnO3/SrTiO3 (LMO/STO) superlattices the LMO/STO relative layer thickness ratio changes the degree of epitaxial strain within the layers and dramatically affects the physical properties of the system, which can be tuned from insulating, mild ferromagnetic, to metallic ferromagnets. Such behaviors are ultimately related to the oxygen - 3d metal bonds and hence to the occupancies of the partially filled 3d bands, which define their oxidation state. In this talk we will review procedures to measure oxidation states in manganites from electron energy loss spectra obtained in the aberration corrected scanning transmission electron microscope, and apply these techniques to imaging subtle O displacements and measure their effects on the electronic properties of LMO/STO interfaces. These results will be discussed and combined with density functional theory, in connection with the magnetotransport properties.